Servo driver selection

Gatesy wrote: I did have a look inside one a while, and I seem to remember it was like a glass disc with 4 tracks etched on to it?????

That sounds like the 4-track gray-code, as has been discussed.

Do these encoders give out a standard encoder output, or is it unique to Fanuc?

Gatesy wrote: Do these encoders give out a standard encoder output, or is it unique to Fanuc?

All Fanuc "Red Cap" encoders are proprietary to some degree. The original version had standard AB quadrature plus index, but the commutation signals were proprietary. A later version added battery backup and a position memory to the encoder, so the control could set the home position anywhere, and then when the control was powered up, the encoder could send all the quadrature counts from home to wherever it was at power-off (of the control). This includes the number of full turns from the home position. You did not need to perform a home move sequence each time the control was powered up.
These are called the ABS encoders, and have an extra 2-pin connector on the encoder dust cover. The AB quadrature and index signals on these encoders are industry compatible. They are seen a lot on robots, which can be very hard to home due to the collision risk.

Then, they came up with serial encoders. The problem with quadrature encoders is the count rates get very high when they are moved fast. Some of the latest serial encoders give resolutions of one million counts/rev. If such an encoder is spun at 2000 RPM (33.3 revs/second) then it would give 33.3 million counts/second, which few CNC controls could handle. So, they decided to have the encoder send the absolute position, incuding nuber of turns from home, all the time, rather than the incremental counts. This protocol is totally proprietary.

Jon

Gatesy wrote:
The numbers on the encoder casings are A860-0308-T112 And they are 2500P

This exact model is not in my cross reference, but it seems like it must be from the first series, and will have the traditional AB and Z signals, and the 4 commutation signals. So, it is not a serial encoder.

Jon

Thanks Jon

I have often wondered what the difference is between the different types.

I have found the encoders I have are also listed as A290-0521-V542 incremental pulse coder

Gatesy wrote: Thanks Jon

I have often wondered what the difference is between the different types.

Oh, it is BAD!!! They made THOUSANDS of different types of encoders, drives, motors, it is VERY confusing.

I have found the encoders I have are also listed as A290-0521-V542 incremental pulse coder

Yeah, see, A290 is a "catalog number" which is different from a "reference number". The A860 is the Reference number. I don't have your A290-0521-V542 number in my cross reference. But, I might be able to look it up from the motor number, which also contains the encoder type info.

Jon